The invention is directed to a process using ion exchangers for obtaining L-malic acid from the reaction mixtures resulting from the enzymatic reaction of fumaric acid to form L-malic acid.
It is known to produce L-malic acid by enzymatic reaction of fumaric acid, namely the fumaric acid is generally employed as a salt in aqueous solution so that the resulting reaction mixtures contain the malic acid and unreacted fumaric acid as their salts. Besides it is known to obtain pure L-malic acid from these reaction mixtures by first separating off the unreacted fumaric acid by acidification, then separating off the L-malic acid as the calcium salt in the form of dihydrate, then dissolving this salt by means of sulfuric acid, successively leading the solution over an acid ion exchanger and base ion exchanger for the purpose of removal of the calcium and sulfate ions and finally separating off the malic acid (German No. OS 2450137, the entire disclosure of which is hereby incorporated by reference and relied upon). The process is cumbersome and expensive and the yield of L-malic acid is unsatisfactory.